﻿Yol. 64.] AKD PHYSIOGRAPHY OF AVESTEEK" LIBEEIA. 315 



Of the dyke-rocks five specimens have been sliced for exami- 

 nation. Of these, two were collected by Mr. Byrde, and are from 

 the lighthouse-rock at Grand Basa, and from Hartford on the 

 St. John Eiver ; the others are from Sulwangei, Burrorje, and Horpa 

 Town. Although varying in grain, these rocks are singularly con- 

 stant in petrological characters; they are ophitic dolerites 

 consisting of transparent laths of bytownite or labradorite, a rather 

 reddish augite, and ilmenite. In the example from Grand Basa 

 there is a little interstitial micropegmatite, and in that from Horpa 

 are some pseudomorphs apparently of olivine. 



The numerous dykes met with to the north of Kaka, in the Po 

 Range, between Bellapafamu and Gambrebu, in the neighbourhood 

 of Zow Town, and on the St. Paul River above Punga, do not differ 

 sufficiently the one from the other or from those above mentioned 

 to merit a more detailed examination. 



Conclusions. 

 In conclusion I would suggest : — 



(a) That we have indications in the southern part of the district, 

 namely, Arthington, Whiteplains, Caresburg, and Basa, of a 

 series of garnetiferous gneisses, tremolite-schists, kyanite- 

 schists or gneisses, garnet-graphite-gneisses, etc., associated 

 with others of grauitic type. 



These latter are apparently free from mic recline, and 

 contain a pleochroic pyroxene. 



(6) That these rocks are replaced on the north, that is, around 

 Takwema, Marakorri, Sanoyei, and Kaka, by biotite- 

 gneisses and hornblende-schists, which have an approximate 

 and singularly constant (magnetic) east-and-west foliation- 

 strike. Microcline is common. 



(c) That these old crystalline rocks are cut by an extensive 

 series of basalts and ophitic dolerites, resembling so closely 

 the post-Cretaceous dykes of Southern jSligeria that it is 

 difficult to avoid the conclusion that they are of the same 

 age. 



II. Physiogeaphy. 



The principal features of the physiography of Liberia, as above 

 limited, are the low-lying character of the country, the very 

 gradual rise northwards from the shore-level to at least the latitude 

 of Marakorri (about 7° 13' lat. N.), and in relation to these the 

 mature character of the Lofa, St. Paul, Mahe, Burror, and Junk 

 Hivers. The fall of the St. Paul is about 10 feet per mile (aneroid 

 determinations) over that part of its course which I visited, that 

 is, from MiUsburg (tidal) to Burukai, a distance of nearly 70 miles, 

 along which waterfalls (as distinct from rapids) are rare. 



The tributary and main streams approximate at least in grade ; 



